Quote:

...so that I can sing parts of my compositions with a choir in back of me, for example ?




Isn't that something that BIAB/RB excels at?

I would start on the Chord Sheet View Window and enter your chord progression, then adjust the Key, Tempo, and Style until you have something relatively close. Look for something with a choir in the style. Perhaps the easiest, regardless of your final instrument choice, would be piano. Then look at your progress in Editable Notation View or Piano Roll View (which allows dragging notes and durations around to suit). Adjust all parameters until you have a backing choir then hit RECORD to add your vocal track. Its really much easier than my explanation makes it out to be.